Liquid crystal panel modules employed in liquid crystal display devices include backlights (see Patent Document 1, for example). In general, a plurality of cold cathode fluorescent lams (hereinafter referred to as CCFLs) or a plurality of external electrode fluorescent lamps (hereinafter referred to as EEFLs) are utilized as a light source for the backlight of the liquid crystal panel module. The backlight utilizing the plurality of CCFLs will be referred to as a CCFL backlight, and the backlight utilizing the plurality of EEFLs will be referred to as an EEFL backlight.
FIG. 11 is a schematic view showing the configuration of a general CCFL backlight.
As shown in FIG. 11, the CCFL backlight 500 includes a plurality of CCFLs 50 arranged parallel to one another. Each CCFL 50 has internal electrodes at its both ends. One ends of the plurality of CCFLs 50 are connected to step-up transformers 40 through ballast capacitors CB, respectively. The other ends of the plurality of CCFLs 50 are grounded. The ballast capacitors CB function as stabilizers.
As described above, in the CCFL backlight 500 of FIG. 11, each CCFL 50 needs the ballast capacitor CB and the step-up transformer 40. This increases the number of components, resulting in higher total cost of the components.
FIG. 12 is a schematic view showing the configuration of a general EEFL backlight.
As shown in FIG. 12, the EEFL backlight 600 includes a plurality of EEFLs 60 arranged parallel to one another. External electrodes are provided at both ends of each EEFL 60. One external electrodes 63A of the plurality of EEFLs 60 are connected to a common step-up transformer 70a, while the other external electrodes 63B of the plurality of EEFLs 60 are connected to a common step-up transformer 70b. The plurality of external electrodes 63A are integrally held by a lamp fixing plate made of metal, while the plurality of external electrodes 63B are also integrally held by a lamp fixing plate made of metal (See Patent Document 2, for example).
Since the external electrodes 63A, 63B of the EEFLs 60 function as stabilizers, the common step-up transformers 70a, 70b can be connected to the respective ends of the EEFLs 60, thus decreasing the number of components. On the other hand, a lighting voltage of the EEFLs 60 having the external electrodes is higher than a lighting voltage of the CCFLs 50 having the internal electrodes. Therefore, the step-up transformers 70a, 70b that differentially operate are connected to the respective ends of the plurality of EFFLs 60. Nevertheless, the EEFL backlight 600 employs fewer components in total than the CCFL backlight 500, resulting in reduced total cost of the components.
[Patent Document 1] JP 2000-162593 A
[Patent Document 2] JP 2004-247277 A